UIC Code 778-4 R
1st Edition, 01.07.1989. Revised Draft 10-09- 2008, 27-11-2008, 14-01-2009, 15-02- 2009, 18-04-2009
Reviewed by the Panel of Structural Experts 04-02-2009
Defects in railway bridges and procedures for maintenance
Union Internationale des Chemins de fer, UIC Internationaler Eisenbahnverband
International Union of Railways
Summary
This leaflet gives guidelines and recommendations covering procedures for the maintenance and strengthening of railway bridges. Arrangements and methods for inspection are presented;
defects are described; methods for monitoring and assessment are given; and procedures for maintenance, repair, strengthening and renewal are defined.
The purpose is to update the 1989 edition of UIC Code 778-4R and to implement results from a European Integrated Research Project (2003-2007) on “Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives” (TIP3-CT-2003-001653) within the 6
thFramework Programme.
Table of Contents
Summary ...2
Table of Contents ...2
1 - Inspection of railway bridges and detection of defects...3
1.1 - General ...3
1.2 - Arrangements for inspection...6
1.2.1 - Detail and frequency ...6
1.2.2 - Routine inspections ...6
1.2.3 - Principal Inspections ...6
1.2.4 - General Inspections...7
1.2.5 - Documents ...8
2 - Defects in existing bridges ...9
2.1 – Definitions ...9
2.2 – Detection and measurements of defects ...9
2.2.1 - Overview of methods and equipment ...9
2.2.2 – Methods for metal bridges...11
2.2.3 – Methods for Masonry Bridges...13
2.2.4 – Methods for Concrete Bridges ...15
2.2.5 – Methods for Bearings and Foundations ...17
2.3 - Classification of defects ...19
3 - Monitoring ...20
3.1 Testing methods: ...20
3.2 Data processing methods:...20
3.3 Sensors: ...20
4 - Methods for Load and Resistance Assessment ...21
5 - Maintenance, repair / strengthening and renovation...22
5.1 - Maintenance ...22
5.2 - Repair ...22
5.3 - Strengthening ...23
5.4 - Renewals ...24
Bibliography...25
Appendix A – Notation ...27
1 - Inspection of railway bridges and detection of defects
1.1 - General
Regular inspection is a means of keeping a constant watch on the daytoday condition of structures, by noting defects as they occur and identifying the cause of any damage discovered.
The actual condition must be compared with the benchmark required for the structure in service.
If it is established from inspection that the structure has only minor defects, these results can be used to specify and organise the necessary maintenance work.
If, however, more extensive damage is discovered, the structure must be repaired and restored to satisfactory condition, and the cause of the damage should be investigated and put to rights (see Figures 1, 2 and 3).
One of the main considerations is that the structure should be in suitable condition to allow the normal movement of rail traffic over the line on which it is located ,with the required level of safety at all times.
If line operating parameters are changed (for example, because of heavier axle loads or higher running speeds), then a knowledge of the actual condition will be a factor in the decision as to whether the structure needs to be strengthened or whether complete renewal is necessary.
Engineers must adopt the engineering solution which will cause least disturbance to rail traffic operations. However, the overall economics of the engineering work must be taken into consideration.
Those responsible for the project and bridge designers should give preference to types of construction which allow easy inspection, maintenance and repair or renovation of the structure throughout its service life.
In the rest of this leaflet, reference will be made to reports produced by the EC-project
“Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives”, carried out between 2003 and 2007. The reports are available from: www.sustainablebridges.net.
For masonry bridges, additional information is given in UIC Code 778-3R (2009) “ Recommendations for the inspection, assessment and maintenance of masonry arch bridges”.
A standard for the terminology for maintenance is given in EN 13306 (2001).
Figure 1. Regular operation and maintenance of bridges. If there are questions regarding safety, serviceability or durability, action can be taken according to Figures 2 and 3.
From SB-GUIDE (2007).
Figure 2. Special stage of operation and maintenance of bridges when there is a special concern regarding . safety, serviceability or durability. After decisions are made and actions taken (the last line in the figure), the bridge is returned to regular operation and maintenance according to
Special stage
Investigation and assessment
BRIDGE ASSESSMENT
(Carried out in phases) Special inspections
supported by more/less advanced tests (quantitative information)
Focused monitoring through
limited time period (quantitative information)
Required performance
confirmed?
Decision making and action taken
Redefine use Intensify monitoring
Replacement Strengthening
and/or repair Regular operation and maintenance
BRIDGE MANAGEMENT
(Administration) Regular inspections
followed by condition assessment (qualitative information)
Optional Structural Health
Monitoring (qualitative information)
Regular, minor maintenance (preventive, corrective)
Bridge Management System
(more/less advanced) Political and economical requirements
(higher loads and speeds, increased traffic volume, extended service life, etc. )
Figure 3. Flow chart for the assessment of existing bridges as part of the process with the special stage of operation and maintenance in Figure 2. Three phases are identified: Initial, Intermediate and Enhanced, depending on the complexity of the questions involved.’ Taken from SB-LRA (2007).
Doubts
PHASE 1 - INITIAL Site visit Study of documents
Simple calculation
PHASE 2- INTERMEDIATE Material investigations Detailed calculations/analysis Further inspections and monitoring
PHASE 3 - ENHANCED Refined calculations/analysis Laboratory examinations and
field testing Statistical modelling Reliability-based assessment Economical decision analysis
Simple strengthening
of bridge Update
maintenance, inspection and monitoring strategy
Redefine use and update maintenance,
inspection and monitoring strategy
Demolition of bridge Strengthening
of bridge Unchanged
use of bridge Doubts confirmed? Yes
Yes Yes
Yes
No No
No
No Compliance with
codes and regulations?
Simple repair or strengthening
solve the problem?
Sufficient load capacity? Acceptable
serviceability?
1.2 - Arrangements for inspection 1.2.1 - Detail and frequency
Inspections should be made with varying degrees of detail and at varying frequencies, depending on the type of inspection and taking account of the nature and previous condition of the structure. Apart from ordinary surveillance when train and track staff continuously monitor the bridge when passing it; a distinction is made between three levels of inspection:
- Routine inspection: Annual inspection from ground level by trained examiner.
- Principal inspection: Refined visual inspection with focus on safety every (2
ndor) 3
rdyear . These inspections can also provide the opportunity for simultaneous special in-depth inspections, not necessarily covering the entire structure, but perhaps for dealing with a particular component or problem area.
- General inspection: Extremely detailed inspection with examination of all parts of the bridge within touching distance (with hammer tapping on concrete surfaces) every 4 to 6 years.
However, the inspection frequency should reflect the nature of the bridge and the defects observed. In practice this means that the inspection frequency will vary according to bridge type and condition. The general inspection should result in production of a full and detailed report on the condition of the structure.
The final inspection made on handover of the structure or before its commissioning, or following major repair work, provides a benchmark for the required condition.
Special equipment and facilities will generally be required for these inspections, during which structures should be subjected to visual examination in order to locate any defects with the aid of special examination techniques.
1.2.2 - Routine inspections
The inspector should be trained and have a basic understanding of bridges.
The standard equipment includes basic tools such as hammers, cameras and lighting facilities.
Foundations should be inspected at low water. Please look down.
1.2.3 - Principal Inspections
The inspector should be aware of the methods given in section 2.2 below.
A principal inspection consists of a visual examination of all accessible parts of the bridge without using special access equipment. All defects which can be visually detected from the ground must be recorded and the condition of the structure must be evaluated in an appropriate manner.
Continuous monitoring may be used to keep a check on particular developments or a new
situation arising between two periodical inspections . By means of such monitoring, defects
which could become a hazard to railway operations can be monitored carefully.
Such inspections may need to be supplemented by information from outside specialists.
Details of methods for monitoring are given in SB-MON (2007) and for masonry bridges in UIC Leaflet 778-3 (2009).
1.2.4 - General Inspections
General inspections should be carried out by bridge experts. They should be assisted by specialist staff, who should be well experienced in carrying out examinations besides having the necessary technical knowledge. They should not only be able to identify defects but also to ensure that their development can be monitored through suitable measurements to determine movements, displacement, reductions in cross-section due to stress-induced corrosion. , etc.
A firstlevel assessment of the capacity of the bridge could be carried out in conjunction with the inspection. Likeliest causes of different damages should be recorded. Need to repair or further inspect or monitor the bridge as well as traffic limitations should be defined in the inspection report.
Suitable means of access to the various parts of the structure, ranging from ladders to special scaffolding, should be arranged. Depending on the topography and on the features of the structure to be inspected (Iength, height, etc.), these aids, depending on the requirements of the railway concerned, may be subdivided as follows:
- For very long viaducts spanning inaccessible terrain, it may be economical to equip the structure, at the construction stage, with an inspection platform, or at least with longitudinal rails on which an inspection vehicle can travel, the latter being brought on site only when required.
- Rail-mounted / lowering platforms. This equipment is mounted on a rail vehicle and has an inspection platform at its outer end, with a system of hydraulically-operated articulated arms that can be controlled and operated either from the platform or from the vehicle.
Such units can be used for full inspections using only one line of a doubletrack section. They are accompanied by a service vehicle of the Pemanent Way Department.
- Lifting platforms mounted on rail, road or road/rail vehicles. These platforms mounted on a rail vehicle, road vehicle or road/rail vehicle, can be moved by rail or road and are provided with an inspection platform located either on the extension of a double articulated arm or on an arm with several telescopic sections. Examinations are carried out either from the inspection platform itself or from the driving cab of the rail, road or road/rail vehicle.
Examples of methods are given in section 2.2 below, in SB-MON (2007), chapter 7 “Monitoring tool-box” and, for masonry bridges, in UIC Code 778-3R (2009).
Special investigations such as the analysis of vibration behaviour to assess the condition of the structure; mineralogical and microscopic analyses to diagnose material conditions, ultrasonic testing or radiography for cables etc., are matters for teams of experts to address.
Preparations should be made beforehand to facilitate inspection, for example:
- cleaning of bearing areas;
- installation of scaffolding;
- removal of certain elements to facilitate inspection of main structural components;
- for piers and foundations it may be necessary to use divers.
1.2.5 - Documents
Documents such as design drawings, geotechnical surveys, calculations, construction documents and the results of the acceptance inspection of the structure provide basic inputs for the inspections. The documents shall be available during the inspections in paper or digital form (e.g in a lap-top computer)
The reports of subsequent inspections shall be based on the surveys of the actual condition of the structure. They shall contain details of irregularities discovered or of the development of defects revealed by earlier inspections.
Details shall also be given of the maintenance work necessary in the short and long term;
together with any operations carried out since the last inspection.
2 - Defects in existing bridges
2.1 – Definitions
A list of definitions and notations is given in Appendix A
2.2 – Detection and measurements of defects
2.2.1 - Overview of methods and equipment - Visual examination;
- Detection and monitoring of cracks of all kinds by means of recording devices, strain gauges, crackwidth gauges, glued indicators, ultrasonic equipment, measuring shims, extensometers,.
etc.;
- Measurement of deformation under static and dynamic loading, measurement of progressive deformation, measurement of bearing reactions and rotations;
- Levelling;
- Analysis of dynamic behaviour (seismograph or accelerometer).
The following examples of available equipment are given in SB-ICA (2007), Table 5.2. In SB- ICA (2007) there is also a tool box for non destructive testing (NDT) methods with a one-page summary of each method explaining its merits and drawbacks. The background to the tool-box is described in Helmerich et al (2007, 2008a, b). Methods for masonry arch bridges are also given in UIC Code 778-3R (2009).
Table 2.1 Overview of methods and equipment
Visual and Simple Methods
External visual inspection External visual inspection, usually performed regularly in routine surveys or inspections, limited by human factors
Internal visual inspection (video scope)
Internal visual inspection with devices through holes in hidden or covered parts of steel or concrete structures, experience required, inspection limited by the length of the cable
Void volume measurement Evaluation of hollows by air or fluid pressure
Air (Torrent) Permeability Fluid or air permeability of concrete surfaces as measurement of durability,
Cover measurement Depth of reinforcement in concrete structure, thickness of the concrete cover, reliable equipment available on the market
Roughness depth test Investigation of concrete surface roughness Liquid penetrant test Surface cracks in welds of steel connections.
Sclerometric test Hardness of young concrete.From Greek skleroo, harden
Hardness Hardness of steel
Thermal Heat Transfer Transient (active) thermography
Debonding of tiles, plaster, mortar, carbonfibre reinforced polymers (CFRP), determination of humidity/ moisture content
Pulse-phase thermography Debonding, near surface voids with optimised contrast
Acoustic, Electric and Electromagnetic Methods
Acoustic emission Detection of growing active cracks Modified Acoustic Emission
(AE)
Survey of known active cracks, in laboratory-modified AE for search of active cracks
Low strain pile integrity testing
Pile length, integrity Parallel seismic Pile / sheet depth
Cross-hole tomography Soil, parameters, consolidation beneath embankments Cross-hole sonic logging Material quality in foundations
Impulse-radar echo
Radar tomography Thickness of concrete elements, grouting level of tendon ducts, localisation of rebars and tendon ducts
radar
Electrical conductivity Investigation of rebars and tendon ducts Electromagnetic induction Cracks in tendon wires (slightly destructive)
Impulse-radar echo Cracks from point loads, longitudinal cracks, surface cracks due to lack of bond in more layered arches, spandrel wall separation, spalling or mortar loss
Radar tomography Leaching, inner cracks from freeze-thaw-cycling, hollows, moisture (in research)
Ground penetrating radar Evaluation of layers and voids in embankments and subsoil Radar scouring Scouring around stream piles
Electrical conductivity Moisture content, backfill type and quality Electrical conductivity Moisture, soil type
Galvanostatic pulse Corrosion state of reinforcement, properties of cover concrete (moisture, deteriorations)
Linear Polarisation Corrosion state of reinforcement, covercrete thickness (moisture, deteriorations)
Sliding collar Cable-stayed bridges Ultrasonic-echo (US-echo)
Dry coupling using US-array
Thickness measurement, localisation of reinforcement or tendon ducts, voids in RC
Ultrasonic transmission tomography
Localising reinforcement or tendon ducts, voids in the concrete
Impact-echo Thickness measurement, localisisation of reinforcement or tendon ducts, Impact-echo Investigation of crack depth
Ultrasonic-echo Residual thickness of mild and modern steel plates, weld defects, surface cracks, cracks parallel to the surface, surface crack depth, inhomogeneity Ultrasonic-phased array Weld defects, inhomogeneity, corrosion mapping (established by industry) Ultrasonic emission Inclusions and segregations in steel plates
Eddy current inspection Cracks in rivet holes, cracks in very thin metallic plates Combined Ultrasonic
Inspection
Ultrasonic velocity (transit time tomography), Residual stress in rivets Ultrasonic-echo (masonry) Detection of deterioration
Radiographic Methods Radiography with isotopes/
steel (RI)
Detection of cracks in hidden elements and inhomogeneities in modern steel or connections (welds)
Radiography with x-ray/
cobalt
Detection of voids in RC, localisation of reinforcement and tendon ducts Spectral-chemical and Potential Methods
Electrical potential field
measurement Corrosion state of reinforcement Laser-Induced Breakdown
Spectroscopy
Analysis of chemical elements on surface and near surface Sparkle Emission
Spectroscopy
Analysis of chemical elements of the steel Sulphur print
(slightly destructive)
Chemical analysis for identification of the used iron/ steel
Advanced Data Acquisition and Evaluation Methods
Automated scanning system Parallel use of different sensors for NDT-investigation of concrete bridge slabs
Synthetic aperture- focusing technique
Reverse projection of wave images
Data fusion Superposition of results from different NDT-measurements
2.2.2 – Methods for metal bridges Examination on site:
• corrosion and reduction of cross-section:
- measurements of corrosion depth using depth gauges;
- measurements of residual depth by ultrasonic means or by drilling;
- direct measurements of the progress of corrosive attack;
- state of corrosion protection;
• detection and monitoring of cracks in the steel:
- by visual examination with or without dyepenetration technique;
- detection by radiography or ultrasonic method (whenever possible) when looking for non-visible defects;
• detection of loose connections involving rivets and bolts:
- by visual examination;
- by tapping in a careful way so that the rivets do not get harmed - with a torque spanner;
• detection of cracks in welded joints:
- by visual examination using a lamp, with or without dye penetration technique ; - by radiography or ultrasonic methods in cases of doubt.
Laboratory testing to determine:
fatigue, composition, tensile strength, notch ductility, elongation, micrography, testing of weldability.
Attention is drawn to the difficulties involved in taking samples, and to the problem of obtaining representative samples.
Metal sampling should ensure that, with a limited number of investigations and laboratory tests,
the most accurate information can be obtained on the nature and characteristics of the materials used in the structure.
The problem, however, is:
1) that it is often difficult to remove a sufficient amount of steel from structural elements to provide a representative sample;
2) to identify lowstressed structural components for sampling to prevent significant weakening of the structure;
3) whether the sample taken is adequately representative of the structure as a whole (e.g. old iron or steel bridges, in which materials of varying origin have been used on construction or repair).
In Table 2.2 NDT methods are given. A combination of methods is often useful.
Table 2.2. Non Destructive Testing (NDT) Methods for Metal Bridges
The following table gives information about restrictions and limitation of NDT-methods, SB-ICA (2007), Table 5.4.
NDT-Method Investigated details Limitation in use.
Accuracy of the method including characteristics of the material
Remarks
Visual Contamination, loss of material, deterioration, displacements, cracks
Cracks <0.1 mm, only surface observation
Depends on span
Hammer tapping
Listening for audible sounds from tapping the surface with a hammer
Provides an approximate understanding of the condition
Simple and inexpensive
Acoustic Emission (AT)
Propagating cracks 2D/ 3 D-Localisation of active cracks
Not for stable (not propagating) cracks
~ 10% of the distance between sensors
Research level
Eddy current test
Defects in thin layers Max depth 10 mm, local resolution >
2mm,
Only magnetisable materials
Follow safety instructions of the railways when using hand held tools Magnetic
particle test
Surface cracks Crack opening > 0,1 mm, length > 1 mm, crack hole investigation during replacement of rivets
Documentation only with camera
Colour penetration test (PT)
Surface cracks, Remove old colour width > 0,1 mm Length > 1mm
Documentation only with photography
Radiography (RT)
Internal voids in sandwiched elements
Maximum investigated plate thickness:
70 mm
Last phase (3rd) in reassessment Ultrasonic
echo (UT)
Weldroot testing, residual plate thickness, thickness of surface coating
For example:. use of reference grooves for calibration:
Width x depth:
0.11mm x 0.95 mm Depth/width ratio: < 25
General inspection, in all phases of the
reassessment as needed
Ultrasonic array (UT- array)
Internal void depth and lateral dimensions, defect inhomogeneity
Multi-channel systems for adaptation to special tasks
Last phase (3rd) in reassessment
The EU (JRC) has published recommendations for the Assessment of existing steel structures together with the ECCS [EUR23252EN].
2.2.3 – Methods for Masonry Bridges
A UIC project on Masonry Arch Bridges, UIC Masonry (2008), has produced recommendations for inspection, assessment and maintenance of masonry arch bridges, UIC Code 778-3R (2009).
Standard methods used involve:
- In-situ visual examination (if necessary with the aid of an endoscope);
- Sampling, and laboratory tests to determine porosity, density, frost sensitivity, composition, weathering.
In Table 2.3 NDT methods are given. A combination of methods is often useful.
Table 2.3. Non Destructive Testing (NDT) Methods for Masonry Bridges
The following table gives information about restrictions and limitation of NDT-methods, SB-ICA
(2007), Table 5.4. Information is also given in UIC Code 778-3R (2009) Tables 3.1- 3.6
NDT-Method Investigated details Limitation in use.
Accuracy of the method including characteristics of the material
Remarks
Visual Qualitative values:
geometry cracks (length, depth), heavy
displacements, longitudinal/ diagonal cracks in the barrel, vegetation, drainage, humidity, heavy settlement
Cracks <1.0 mm, only surface observation. An endoscope may be useful
Inspection time depends on span
Hammer tapping
Listening for audible sounds from hammer- tapping the surface
Provides an approximate understanding of the condition
Simple and inexpensive
Radar-echo 500 MHz, 900 MHz, (Ground penetrating radar, Geo- radar, Impulse radar)
Arch barrel and wing wall thickness, retaining wall inhomogeneity, embankments/ hollows, heavy deterioration Humidity,
Metal inclusions (anchors)
Appropriate for depth maximum 2 m (lower frequencies)
Defect size: in homogeneous material:
~ 5% of the depth, in heterogeneous material: ~ 10 % of the depth,
Access from one side, Use in assessment phase 3
Radar echo 200-500Hz
Back fill thickness, ballast thickness
< 5 m depth
in heterogeneous material: ~ 10 % of the depth,
EU-funded project Saferail has developed new wagon with 4 antennas Ultrasonic
echo (US) (US-array without coupling agent):
transversal: 50 kHz
longitudinal:
100 kHz
Local inhomogeneity, Thickness,
Metal inclusions
Depending on the condition of the masonry
Defect size: 10-30 mm
Train traffic noise, building activities such as drilling, anchor dysfunction or other noise can influence acoustic signal acquisition
Access from one side:
Depending on the task to solve: Frequency 50-300 kHz.
Assessment phase 3
Acoustic emission
Localisation of active cracks
10 % of the sensor distance in the array, Influenced by low temperature, defects, deformation rate
Method feasible, No final standards, since research is ongoing SIP-spectral
induced polarisation
Humidity, inhomogeneity visualised in 2D- conductivity images
Applicable to backfill, masonry
Flat-jack test Single or double*
Determination of stress under service in the masonry
Local near surface, information about the stress behaviour/elasticity of the masonry, locally destructive resolution
~ 0,1 N/ mm2
Standard test (Rilem, ASTM)
Hole-drilling method*
Stress-strain behaviour in one single point
Only local and superficial information Accuracy of strain gauge: + 1 µε
2.2.4 – Methods for Concrete Bridges
For reinforced- concrete bridges (in-situ frames, slab bridges and girder bridges):
detection of inadequate reinforcement: number, diameter and location of bars, fracture and corrosion of reinforcement, concrete cover (depth gauge);
detection of cavities within the structure.
measurement of depth of carbonisation, measurement of cracks, strength measurement;
testing of samples in laboratory:. compressive strength, composition, density, porosity, frost sensitivity, tensile strength, degree of weathering.
For prestressed-concrete bridges (bridges with channels/ducts, slab bridges, girder bridges, box- girder bridges, etc.):
• detection of inadequate reinforcement and of cavities in the bridge structure as for reinforcedconcrete bridges;
• detection of defects in cable ducts: incorrect alignment of ducts and faulty grouting, fracture and corrosion;
• detection of defects in prestressing strands and wires: number, dimensions, position, fracture and corrosion.
• testing of samples in the laboratory: tensile strength, fatigue, composition, elongation, flexural strength, weldability.
Additional measures for steel/concrete composite bridges:
• detection of separation between steel and concrete by radiography (in particular gammagraphy),
In Table 2.4 NDT methods are given. A combination of methods is often useful.
Table 2.4. Non Destructive Testing (NDT) Methods for Concrete Bridges
The following table gives information about restrictions and limitation of NDT-methods, SB-ICA
(2007), Table 5.4.
NDT-Method Investigated details Limitation in use.
Accuracy of the method includingcharacteristics of the material
Remarks
Visual Contamination, loss, deterioration,
displacements, cracks
Cracks <0.1 mm, only surface observation, loose cover
Inspection time depends on span
Hammer tapping Listening for audible sounds from hammer- tapping the surface
Provides an approximate understanding of the condition
Simple and inexpensive
Radar-echo 500 MHz, 900 MHz, 1.5 GHz
(Ground- penetrating radar, Geo- radar, impulse radar)
Girder-web thickness, Slab thickness,
Embankment/ Retaining wall reinforcement, Tendon ducts, Inhomogeneity, Humidity,
Metal inclusions (anchors)
Appropriate for depth max. 2 m Defect size: in homogeneous material: ~ 5% of the depth, in heterogeneous material:
~ 10 % of the depth,
Dense reinforcement near surface prevents deep penetration.
Access from one side, Use in assessment phase 3
Radar
transmission 500 MHz, 900 MHz, 1.5 GHz
Girder web thickness, Reinforcement of tendon ducts,
Inhomogeneity
Method in course of development, better imaging of inhomogeneity expected
Research level, Access from both sides
Ultrasonic echo (US)
(US-array without coupling agent):
transversal: 50 kHz
longitudinal: 100 kHz
Reinforcement, tendons location, grouting of tendons,
Local inhomogeneity, Thickness,
Metal inclusions
Depth: 5-40 cm Defect size: 10-30 mm
Train traffic noise, building activities such as drilling, anchor dysfunction or other noise can influence the acoustic signal acquisition,
Access from one side:
Depending on the task to be solved: Frequency 50-300 kHz.
Assessment phase 3
Acoustic emission
Localisation of active cracks
10 % of the sensor distance in the array, Influenced by
low temperature, defects, deformation rate
Method feasible, No final standards, since research is ongoing Ultrasonic air
coupling
Voids Reflected surface waves influence
the emitted waves
Research level
Impact-echo Thickness, delamination between two concrete layers, location of voids, quantification of cracks
Train traffic noise, building activities such as drilling, anchor dysfunction or other noise can influence the acoustic signal acquisition,
Surface waves may influence the result, solution: IE in transmission
Active thermo- graphy
Near subsurface voids, delamination, moisture, plaster delamination, control of strengthening measures
Safe , no radiation, Accuracy depends on depth of the void, camera, distance and further limits, for example: 1m2: 65000 pxl: + 1 cm2
No moving / scanning technique
Radiography (cobalt, γ-ray)
Metal inclusions, cables, wires, tubes
Defect size ~20 x 1-2 mm,
Restriction due to radiation, no traffic during test
Last phase (3rd) in reassessment
2.2.5 – Methods for Bearings and Foundations A – Bearing defects
Bearings are treated in EN 1337 (2000), which addresses the following topics : - Bearings,
- Structural members, - Structural design, - Structural systems, - Rocker bearings, - Roller bearings,
- Cylindrical-roller bearings,
- Mountings (bearing components), - Dimensions,
- Bridges, -Joints,
- Sliding joints, - Movement joints, - Components, - Construction, - Symbols.
Recommendations are also given by the Association for Bearings, see VHFL (2009).
1 - Functional defects:
- examination on site, visual and aural;
- measurement of the positioning and of deformation of the bearing elements;
- inadequate sliding or rolling movement, excessive transverse or longitudinal displacements, tilting or axial movement of the roller track.
- dirt around bearings,
2 - Material defects:
- chemical; mechanical and metallurgical testing of samples.
- cracking of mechanical or elastomeric parts - corrosion
3 - Defects in bearing fasteners:
- detection of loose baseplates or of bedding-mortar break-up.
B – Defects in foundations
1 - Methods applicable to all types of foundations:
- visual examination on site, where necessary after excavation of inspection pits;
- measurements of tilting with the aid of plumb lines, and twist measurements using deflection meters (inclinometers);
- measurements of twist at the bearings;
- ground investigation with the aid of soil samples (penetrometer, pressure gauge);
- examination of borings:
water pressure tests, visual examination (endoscope, TV camera), recording of the various parameters with the aid of probes.
2 - Specific methods applicable to underwater foundations : - visual examination and probing by divers or frogmen;
- depth soundings (underwater topography) and recording of the bottom bed profile, adjacent to the foundations, repeated at regular intervals to determine bed profile patterns;
- underwater cameras and video recordings ;
- use of dyes to follow the route of water courses and locate places where the water reappears.
Examples of methods for foundations and transition zones are given in SB-ICA(2007), chapter 9.
C – Waterproofing defects - Visual examination:
• Looking for traces of water penetration, rust staining. efflorescence, stalactites, white marks along cracks or working joints;
• Localised removal of ballast to detect waterproofing defects or separation of edge sealing
• Inspection of drainage (filter system, outlets, weepholes, drains), - Taking of samples to check permeability under hydrostatic head.
In Table 2.5 NDT methods are given.
Table 2.5. Non Destructive Testing (NDT) Methods for Foundations
The following table gives limitation and interference of NDT-methods with railway operating infrastructure and rough timeconsumption (only for pure measurement without equipment installation), SB-ICA (2007), Table 5.4.
NDT- Method
Investigated details
Limitation in use.
Accuracy of the method including. characteristics of the material
Remarks
Radar echo Radar echo array 200-800 MHz
Soil layers, thickness, scour, humidity
track-bed condition
Penetration depth depending on frequency:
Max. depth 10m,
max. + 5 % of the penetration depth
According to requirements for the test and resolution
SIP Spectral
Sonic-velocity evaluation along a profile on masonry surface
Calibration by means of coring, humidity influences the precission, limited resolution
According to requirements for the test and resolution
Borehole tomography
Integrity of pile foundations, pile length
To measure the integrity, sensors are lovated in a tube paralle to the investigated pile
According to requirements for the test and resolution
Parallel seizmic method
Pile length Influence of construction quality (concrete), stiffness of soil has to be taken into account
According to requirements for the test and resolution